This application relates generally to fan technology for the purpose of moving air and more specifically for the purpose of moving air for applications in thermal management and mixing applications.
Rotary fans to move air for heat transfer applications are the ubiquitous cooling solution in electronics thermal management. Increased power density in electronic products places demands on rotary fan technology to improve air flow rates, reduce size, increase life, lower noise and vibration and reduce power consumption. From this list of conflicting demands, the most challenging appears to be long life. Emerging products such as HBLED lighting can require fan life times of up to 10 years but the bearings used in rotary fans typically provide no more than 3 years of continuous use.
Cantilever fans have the advantage of eliminating the bearings which are typically the life-limiting component of rotary fans. Despite this advantage, cantilever fans fall short on many of the other industry requirements and, thus, have seen little commercialization during the three decades devoted to their development. For example, conventional cantilever fans cannot provide air flow rates comparable to rotary fans in a small form factor due to the large length-to-width ratio required for cantilever blade stability and quiet operation.
Also, it appears that nearly all cantilever fan development has focused on piezo laminations as the form of blade actuation and these materials, such as PZT, contain lead. There are a number of disadvantages associated with using materials that include lead such as the manufacturing health and safety risks and related permit and compliance issues, which contribute to the high cost of PZT materials. Furthermore, products that contain hazardous materials such as lead are less likely to be accepted by customers than alternative products containing no hazardous materials.
In addition, laminated PZT actuators require high voltages for their operation. These high voltages are objectionable to most product OEMs. Multiple laminations can be used to reduce the voltage requirements, but these laminations result in higher manufacturing complexity and cost. Multiple laminations require very high manufacturing tolerances if double cantilevers are used to cancel vibration, because the resonance frequency of each blade must be closely matched. Each lamination layer includes very thinly cut PZT and an adhesive layer. As a result, the precision required to manufacture matching blades increases with the product of the number of layers and increases the high cost of laminated piezo actuators.
A further disadvantage of piezo materials is that their transduction properties change over time resulting in reduced performance and loss of the dual blade matching required to provide low vibration cantilever fans. Transduction properties will also change with the aging of the lamination adhesive layers, resulting in the same loss of performance and vibration issues.
The above disadvantages have prevented cantilever fans from being responsive to the industry's need for new innovative fan technology that can provide cost-effective performance and extended life.